At least 15; more, depending on the gun. If it's the snubby, the basic 5 plus a speed strip and a speedloader are the normal complement. Any of the auto loaders I carry with any frequency has at least 7+ 1, then add at least one spare mag.

With my Sig P228, I usually leave with 15 in the mag. I may or may not take a spare, just depends. Now that I have the M&P .357c, I'll carry the 10 in it with a 15 round spare with an X-grip sleeve on it.

AlabamaConstitution of 1819: That every citizen has a right to bear arms in defence of himself and the state.
The world doesn't owe you anything. It was here first.-Mark Twain
"Life's tough. It's tougher if you're stupid."-John Wayne
Sig P228; Micro Desert Eagle; S&W M&P Compact .357 sig

Most of the time my off-duty carry is a G27 with one spare 23 mag. 9+1 in the 27 and 13 in the spare mag give me 23 rounds. On rare ocassions I carry two spare mags giving me 36. When I carry my G30, it is 9+1 and a spare 21 mag of 13 rounds again giving me 23 rounds. When I carry my 19, it is 15+1 and a spare 17 mag with 17 rounds giving me 33 rounds.

Police Defensive Tactics, Firearms, Carbine Rifle and Taser Instructor
Glock Armorer
NRA Life MemberIt is better to have your gun and not need it, than to need it and not have it!You cannot choose the conditions for a gunfight, so train in all conditions!